Epitaxial wafer and production method thereof

ABSTRACT

A small amount of oxygen is ion-implanted in a wafer surface layer, and then heat treatment is performed so as to form an incomplete implanted oxide film in the surface layer. Thereby, wafer cost is reduced; a pit is prevented from forming in a surface of an epitaxial film; and a slip is prevented from forming in an external peripheral portion of a wafer.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/483,439, filed Jun. 12, 2009, which is expresslyincorporated herein by reference in its entirety. Additionally, thepresent application claims priority to Japanese Application No.2008-161026, filed Jun. 19, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an epitaxial wafer and a method ofproducing the same. More specifically, the present invention relates toan epitaxial wafer employing no silicon wafer having a complete SOIstructure, allowing high-precision thinning of the epitaxial wafer, andachieving cost reduction. The present invention also relates to a methodof producing the epitaxial wafer.

2. Description of the Related Art

A SOI (silicon on insulator) wafer is known, in which an implanted oxidefilm is formed in a surface layer of a silicon wafer, and thereby anactive layer having monocrystalline silicon is formed on a wafer surfaceside of the implanted oxide film. Further, a SIMOX (Separation byIMplanted OXygen) wafer has been developed as one type of the SOI wafer.The SIMOX wafer is provided with an ion-implanted layer, which is formedby ion-implanting oxygen in the surface layer of the silicon wafer fromthe wafer surface. After the forming of the ion-implanted layer, thesilicon wafer is heat-treated, and thereby the ion-implanted layer isprovided as an implanted oxide film (implanted silicon oxide film).

An epitaxial SIMOX wafer, which is a SIMOX wafer having an epitaxialfilm grown on a surface thereof, is heavily used as a wafer for CIS(CMOS Image Sensor), which is one type of an image sensor (PatentLiterature 1, for example). The image sensor is a device that capturesimage information by utilizing photosensitive characteristics of asemiconductor. CIS absorbs light that has captured an external image,and integrates photocharge using a photodiode, which is a lightreceiving element. A device is formed on the surface of the epitaxialSIMOX wafer for CIS in a device forming process. A silicon wafer is thenattached to the surface of the epitaxial film. Subsequently, the SIMOXwafer is ground and polished, or etched, from a rear side thereof, andthus is reduced in the thickness. Thereby, a wafer is provided, in whicha device is implanted on the rear side of the epitaxial film (a locationsandwiched by the attached wafer).

Oxygen is ion-implanted herein under conditions of a temperature of 200°C. to 600° C.; an implantation energy of 20 keV to 220 keV; and an ionimplantation amount of 1.5×10¹⁷ atoms/cm² to 2×10¹⁸ atoms/cm². Theimplanted oxide film is used as a polishing stopper or an etchingstopper in a process in which the wafer is thinned from the silicon tothe implanted oxide film. Material properties are capitalized on herein,including a difference in hardness between oxide silicon and silicon,which causes a change in polishing resistance of the wafer; and adifference in an etching rate between oxide silicon and silicon,relative to an etching solution, which causes a change in an etchingspeed.

-   [Patent Literature 1] Japanese Patent Laid-open Publication No.    2005-333052

As described above, the conventional CIS wafer has the SIMOX wafer as amain body and the oxygen ion implantation amount of 1.5×10¹⁷ atoms/cm²to 2×10¹⁸ atoms/cm². Thus, when ions are implanted presumptively whenparticles are deposited on the wafer surface, a defect occurs in whichthe implanted oxide film breaks in a portion associated with theparticles. The defect causes a pit in the wafer surface when theion-implanted layer is annealed at high temperature. Specifically, whenthe ion-implanted layer changes to the implanted oxide film in the hightemperature annealing, a film thickness increases in a portion excludingthe defective potion, along with oxidation of silicon. Accordingly, apit is formed in the portion of the silicon wafer, the portion beingassociated with the defective portion. Consequently, a pit is formed inthe surface of the epitaxial film at the time of epitaxial growth, thuscausing an increase in surface detects of the epitaxial film. Theproblem occurs since the silicon grows in accordance with a shape of thewafer surface.

Further, when the epitaxial SIMOX wafer is produced, oxygen ions are notimplanted in a chamfered portion (external peripheral portion) of thewafer. Thus, no implanted oxide film exists in the external peripheralportion of the wafer. Consequently, unevenness in temperature in theexternal peripheral portion of the wafer increases the thickness of theexternal peripheral portion of the wafer, which has no implanted oxidefilm, of the epitaxial film, thus forming a slip in the externalperipheral portion of the wafer.

In addition, the conventional CIS wafer has the epitaxial film grown onthe surface of the SIMOX wafer having the implanted oxide film. For theCIS wafer, it is thus required, according to a SIMOX wafer productionmethod, that the ion-implanted layer be heat-treated at a hightemperature of 1,300° C. or higher and that high temperature annealingbe performed to form the implanted oxide film formed from a siliconoxide film. Consequently, expenses are increased for a high temperatureannealing device, particularly for a SiC member, thus leading to a sharpincrease in production cost of the epitaxial SIMOX wafer.

BRIEF SUMMARY OF THE INVENTION

As a result of diligent research, the inventors have found that allproblems described above can be solved with an epitaxial wafer having anoxygen ion implantation amount less than a conventional amount andprovided with an incomplete implanted oxide film, in which siliconparticles and silicon oxides mixedly exist; and thus completed thepresent invention. A conventional epitaxial SIMOX wafer has an implantedoxide film (complete implanted oxide film) sequentially provided to anentire area of a wafer surface, excluding an external peripheral portionof the wafer.

The present invention prevents a surface defect from occurring in anepitaxial film, the surface defect being caused by particles depositedon a wafer surface at the time of oxygen ion implantation. The presentinvention also prevents a slip from forming in an external peripheralportion of the wafer, the slip being caused by unevenness in temperaturein the external peripheral portion of the epitaxial film. In addition,the present invention is intended to provide an epitaxial wafer and aproduction method thereof, the epitaxial wafer having a gettering siteof metal impurities and the like and capable of reducing waferproduction cost.

The present invention relates to an epitaxial wafer including anepitaxial film grown on a surface of a silicon wafer; and an incompleteimplanted oxide film formed in a surface layer of the silicon wafer, theincomplete implanted oxide film being mixedly provided with siliconparticles and silicon oxides and being formed by ion-implanting oxygenfrom the surface of the silicon wafer and heat-treating the siliconwafer after the ion implantation.

The oxygen ion implantation amount is reduced, compared with a case ofthe implanted oxide film of the conventional epitaxial SIMOX wafer. Theion-implanted portion is heat-treated when a temperature is lower thanconventional high temperature annealing, such as, for example, at thetime of epitaxial growth. Thereby, the incomplete implanted oxide filmis formed in the surface layer of the silicon wafer. Different from thecase of the conventional implanted oxide film, in which silicon oxidesare provided sequentially, the incomplete implanted oxide film thushardly experiences an increase in oxide film thickness associated withsilicon oxidation. Consequently, even when ions are implantedpresumptively when particles are deposited on the wafer surface, andthus the oxide film breaks in the wafer surface layer, a pit can beprevented from forming in the wafer surface, and eventually from formingin a surface of the epitaxial film grown on the wafer surface. Thereby,a surface defect of the epitaxial film can be prevented, the surfacedefect being caused by deposition of particles on the wafer surface atthe time of ion implantation. Further, the oxygen ion implantationamount is less compared with the epitaxial SIMOX wafer having theconventional implanted oxide film, and high temperature annealing iseliminated. Thus, cost can be reduced compared with the epitaxial SIMOXwafer.

In addition, the present epitaxial wafer causes no difference in agrowth rate of the epitaxial film in the wafer surface at the time ofepitaxial film growth, the difference being between in an area providedwith the incomplete implanted oxide film and in an area of the externalperipheral portion of the wafer. No difference is caused because of eventemperature distribution. Different from the epitaxial SIMOX waferhaving the conventional implanted oxide film, it is thus unlikely thatthe film thickness increases in the external peripheral portion of theepitaxial film, and thereby a slip can be prevented from forming in theexternal peripheral portion of the wafer. Further, the incompleteimplanted oxide film also serves as a gettering site of metal impuritiescontained in the silicon wafer. Thus, the silicon wafer as well as adevice can be prevented from metal contamination.

The epitaxial wafer is a different type wafer from the epitaxial SIMOXwafer in view of the presence of the implanted oxide film. Specifically,the epitaxial wafer is implanted in the surface layer thereof with theincomplete implanted oxide film, in lieu of the implanted oxide film. Amonocrystalline silicon wafer can be employed as the silicon wafer. Thesurface of the silicon wafer is mirror-polished. A diameter of thesilicon wafer is, for example, 200 mm, 300 mm, 450 mm, or the like.

The phrase “heat-treating the silicon wafer” refers to heat treatment ata temperature that allows the incomplete implanted oxide film to form inthe surface layer of the silicon wafer (900° C. to 1,200° C.). Forinstance, heat treatment at the time of epitaxial film growth, heattreatment in a device process, and the like may be employed. The“surface layer of the silicon wafer” refers to a depth range of 0.05 μmto 0.5 μm from the surface of the silicon wafer. A depth of less than0.05 μm increases surface defects of the silicon wafer. When the depthexceeds 0.5 μm, a commercially available ion implantation device can notbe used, and a special implantation device having a larger ionimplantation energy is required.

The “incomplete implanted oxide film” refers to an incomplete siliconoxide film implanted in the surface layer of the silicon wafer. Further,the “incomplete implanted oxide film” has silicon oxides and siliconparticles mixed at a predetermined ratio, the silicon oxides includingdeposited oxides, zonal oxides, and the like formed from SiO_(x)including SiO₂, the silicon particles being granulated silicon in thesilicon wafer due to oxygen ion implantation. The incomplete siliconoxide film refers to a state in which a silicon oxide film is providednon-sequentially (intermittently) in an entire area of the ion-implantedlayer. The incomplete implanted oxide film has a thickness of 0.05 μm to0.5 μm. When the thickness is less than 0.05 μm, the film cannotfunction sufficiently as an end point detector at the time of thinningof the silicon wafer. When the thickness exceeds 0.5 μm, the oxygen ionimplantation time is extended, thus causing reduction in productivity ofthe epitaxial wafer and leading to cost increase. The “surface side of asilicon wafer relative to the incomplete implanted oxide film” refers toa portion in the wafer surface layer between the incomplete implantedoxide film and the wafer surface.

The present invention relates to the epitaxial wafer, in which theincomplete implanted film is sequentially formed across an area in whichoxygen is ion-implanted, of the silicon wafer, by ion-implanting theoxygen in the silicon wafer from the surface thereof, and thenheat-treating the silicon wafer. The phrase “across an area in whichoxygen is ion-implanted, of the silicon wafer” refers to an entirety ofa flatness quality area, which does not include a wafer chamferedportion.

The present invention relates to a production method of an epitaxialwafer including implanting oxygen ions from a surface of a siliconwafer, and thus forming an ion-implanted layer in a surface layer of thesilicon wafer; growing an epitaxial film on the surface of the siliconwafer immediately after the ion implantation; and concurrently heatingthe wafer in the epitaxial growth, and thus heat-treating theion-implanted layer. Thereby, an incomplete implanted oxide film isformed, the incomplete implanted oxide film being mixedly provided withsilicon particles and silicon oxides; and an active layer is formed on asurface side of the silicon wafer relative to the incomplete implantedoxide film.

At the time of ion implantation, a less amount of oxygen ions isimplanted in the surface layer of the silicon wafer than theconventional epitaxial SIMOX wafer. Further, the ion-implanted layer isheat-treated concurrently with the epitaxial growth, which is performedat a lower temperature than high temperature annealing of the epitaxialSIMOX wafer. Thereby, the incomplete implanted oxide film is formed inthe surface layer of the silicon wafer. Unlike the conventionalimplanted oxide film, which does not contain silicon particles and issequentially provided with silicon oxides, the film thickness of theincomplete implanted oxide film thus hardly increases along withoxidation of silicon.

Consequently, even when ions are implanted presumptively when particlesare deposited on the wafer surface, and thus the oxide film breaks inthe wafer surface layer, a pit can be prevented from forming in thewafer surface, and eventually from forming in the surface of theepitaxial film grown on the wafer surface. Thereby, a surface defect ofthe epitaxial film can be prevented, the surface defect being caused bydeposition of particles on the wafer surface at the time of oxygen ionimplantation. Further, the oxygen ion implantation amount is lesscompared with the epitaxial SIMOX wafer having the conventionalimplanted oxide film, and high temperature annealing is eliminated.Since no high temperature annealing device is required, cost can bereduced compared with the epitaxial SIMOX wafer.

In addition, unlike the conventional wafer, no difference is caused inthe growth rate of the epitaxial film in the wafer surface at the timeof epitaxial growth, the difference being between in the area providedwith the implanted oxide film and in the remaining area of the externalperipheral portion of the wafer. Different from the epitaxial SIMOXwafer having the conventional implanted oxide film, it is thus unlikelythat the film thickness increases in the external peripheral portion ofthe epitaxial film, and thereby a slip can be prevented from forming inthe external peripheral portion of the wafer. Further, the incompleteimplanted oxide film also serves as a gettering site of metal impuritiescontained in the silicon wafer. Thus, the silicon wafer as well as adevice can be prevented from metal contamination.

The ion implantation may be performed in any ion implantation method ofa SIMOX process, including a low energy method (100 keV or less), a lowdose method, and a modified low dose method. In any method employed, itis preferable that the oxygen ion implantation amount be 50% to 80% ofthat in the associated SIMOX process. A heating temperature of the waferat the time of oxygen ion implantation is 200° C. to 600° C., forexample. When the temperature is less than 200° C., large oxygenimplantation damage remains in the surface layer of the silicon wafer.When the temperature exceeds 600° C., an outgassing amount from an ionimplantation device increases.

An oxygen implantation energy is 20 keV to 220 keV. When theimplantation energy is less than 20 keV, surface defects of the siliconwafer increase. When the implantation energy exceeds 220 keV, acommercially available ion implantation device can not be used, and aspecial implantation device having a larger ion implantation energy isrequired. An oxygen ion implantation amount is 1×10¹⁵ atoms/cm² to4×10¹⁷ atoms/cm². When the implantation amount is less than 1×10¹⁵atoms/cm², the film cannot function sufficiently as an end pointdetector at the time of thinning of the silicon wafer. When theimplantation amount exceeds 4×10¹⁷ atoms/cm², the oxygen ionimplantation time is extended, thus causing reduction in productivity ofthe epitaxial wafer and leading to cost increase. An oxygen ionimplantation depth is 0.05 μm to 0.5 μm. The oxygen ion implantation maybe performed only once or for a plurality of times. Further, oxygen ionsmay be implanted at a plurality of implantation energies.

The phrase “immediately after the ion implantation” refers to no otherheat treatment process provided between the ion implantation and thesubsequent epitaxial growth. Monocrystalline silicon can be used asmaterial of the epitaxial film formed in the epitaxial growth. Types ofepitaxial growth generally include vapor phase epitaxy (VPE), liquidphase epitaxy (LPE), and solid phase epitaxy (SPE). For siliconepitaxial growth in particular, a chemical vapor deposition (CVD) methodis mainly employed in view of crystallinity of a growth layer, massproduction capability, ease of machine use, simplicity of structureforming of a variety of devices, and the like.

In the CVD method for silicon epitaxial growth, for example, a sourcegas containing silicon is introduced into a reactor along with a carriergas (normally, H₂ gas); and silicon, which is produced in pyrolysis orreduction of the source gas, is deposited on a silicon monocrystallinesubstrate (produced based on a CZ method) heated to a temperature of1,000° C. or higher. Among numerous compounds containing silicon, fourtypes including SiH₄, SiH₂Cl₂, SiHCl₃, and SiCl₄ are generally used inlight of purity, reaction speed, ease of handling, and the like.Examples of an epitaxial growth furnace to be used may include, forexample, a radiofrequency induction heating furnace, a lamp heatingfurnace, and the like. A thickness of the epitaxial film is 1 μm to 20μm. When the thickness is less than 1 μm, a device cannot be formed onthe epitaxial film. When the thickness exceeds 20 μm, productivity ofthe epitaxial wafer reduces, thus incurring cost increase.

An epitaxial growth temperature (wafer heat treatment temperature) is1,000° C. to 1,200° C. When the temperature is less than 1,000° C.,crystallinity of the epitaxial film is deteriorated. When thetemperature exceeds 1,200° C., a slip is likely to form in the externalperipheral portion of the wafer. An epitaxial growth time (waferheat-treatment time) is 1 to 20 minutes. When the time is less than 1minute, a predetermined epitaxial film cannot be obtained. When the timeexceeds 20 minutes, a slip is likely to form in the external peripheralportion of the wafer.

The present invention relates to a production method of an epitaxialwafer including implanting oxygen ions from a surface of a siliconwafer, and thus forming an ion-implanted layer in a surface layer of thesilicon wafer; heat-treating the ion-implanted layer immediately afterthe ion implantation, and thereby forming an incomplete implanted oxidefilm mixedly provided with silicon particles and silicon oxides, and anactive layer on a surface side of the silicon wafer relative to theincomplete implanted oxide film; and growing an epitaxial film on thesurface of the silicon wafer immediately after the heat treatment.

In the ion implantation, a less amount of oxygen ions is implanted inthe surface layer of the silicon wafer than the conventional epitaxialSIMOX wafer. In the heat treatment of the ion-implanted layer, annealingis performed at a lower temperature than high temperature annealing ofthe epitaxial SIMOX wafer. Thereby, the incomplete implanted oxide filmis formed in the surface layer of the silicon wafer. Unlike theconventional implanted oxide film, the film thickness of the incompleteimplanted oxide film thus hardly increases along with oxidation ofsilicon.

Consequently, even when ions are implanted presumptively when particlesare deposited on the wafer surface, and thus the oxide film breaks inthe wafer surface layer, a pit can be prevented from forming in thewafer surface, and eventually from forming in the surface of theepitaxial film grown on the wafer surface. Thereby, a surface defect ofthe epitaxial film can be prevented, the surface defect being caused bydeposition of particles on the wafer surface at the time of oxygen ionimplantation. Further, the oxygen ion implantation amount is lesscompared with the epitaxial SIMOX wafer having the conventionalimplanted oxide film, and high temperature annealing is eliminated.Since no SiC member for high temperature annealing is required, cost canbe reduced compared with the epitaxial SIMOX wafer. Annealing isperformed immediately after the ion implantation, and the epitaxialgrowth is performed subsequently. Thereby, oxygen deposited in theannealing serves as a gettering site, thus allowing production of a highquality epitaxial film.

In addition, unlike the conventional wafer, no difference is caused inthe growth rate of the epitaxial film in the wafer surface at the timeof epitaxial growth, the difference being between in the area providedwith the implanted oxide film and in the remaining area of the externalperipheral portion of the wafer. Different from the epitaxial SIMOXwafer having the conventional implanted oxide film, it is thus unlikelythat the film thickness increases in the external peripheral portion ofthe epitaxial film. Thereby, a slip, which is caused by unevenness intemperature, can be prevented from forming in the external peripheralportion of the wafer. Further, the incomplete implanted oxide film alsoserves as a gettering site of metal impurities contained in the siliconwafer. Thus, the silicon wafer as well as a device can be prevented frommetal contamination.

A wafer heating temperature in the annealing for forming the incompleteimplanted oxide film is 900° C. to 1,200° C. When the temperature isless than 900° C., an oxygen deposition amount is low. When thetemperature exceeds 1,200° C., a special annealing furnace is requiredfor ultra-high temperature annealing. A wafer heat-treatment time in theannealing is 0.5 to 4 hours. When the time is less than 0.5 hour, theoxygen deposition amount is low. When the time exceeds 4 hours,productivity of the epitaxial wafer reduces, thus incurring costincrease.

The present invention relates to a production method of an epitaxialwafer including implanting oxygen ions from a surface of a siliconwafer, and thus forming an ion-implanted layer in a surface layer of thesilicon wafer; growing an epitaxial film on the surface of the siliconwafer immediately after the ion implantation; and heat-treating theion-implanted layer immediately after the epitaxial growth, and therebyforming an incomplete implanted oxide film mixedly provided with siliconparticles and silicon oxides, and an active layer on a surface side ofthe silicon wafer relative to the incomplete implanted oxide film.

The annealing is performed after the epitaxial growth (including heattreatment in a device process). The epitaxial film can thus be producedhaving a low oxygen deposition amount and a small surface roughness,compared with a case in which epitaxial growth is performed afterannealing. The wafer heating temperature and heat-treatment time in theannealing are the same as in claim 4.

The present invention relates to the production method of the epitaxialwafer, in which the ion implantation is performed at a heatingtemperature of the silicon wafer of 200° C. or higher and an oxygen ionimplantation amount of 1×10¹⁵ atoms/cm² to 4×10¹⁷ atoms/cm².

When the wafer heating temperature in the ion implantation is less than200° C., damage at the time of oxygen implantation remains in the wafersurface layer. A preferable heating temperature in the ion implantationis 300° C. to 600° C. When the ion implantation is performed at a lowtemperature of 200° C. to 300° C., an effect can be obtained in which anoxygen deposition amount is increased. The similar effect is obtained ina case in which the ion implantation is performed twice as described inclaim 7. When the oxygen ion implantation amount in the ion implantationis less than 1×10¹⁵ atoms/cm², the film cannot function sufficiently asan end point detector at the time of thinning of the silicon wafer. Whenthe implantation amount exceeds 4×10¹⁷ atoms/cm², the oxygen ionimplantation time is extended, thus causing reduction in productivity ofthe epitaxial wafer and leading to cost increase.

The present invention relates to the production method of the epitaxialwafer, in which the ion implantation includes ion-implanting oxygen inthe surface layer of the silicon wafer at a heating temperature of thesilicon wafer of 200° C. or higher and an oxygen ion implantation amountof 1×10¹⁵ atoms/cm² to 4×10¹⁷ atoms/cm², and thereby forming an oxygenion-implanted layer; and ion-implanting oxygen on the wafer surface sideof the oxygen ion-implanted layer after the forming of the ion-implantedlayer, at a heating temperature of the silicon wafer of less than 200°C. and an oxygen ion implantation amount of 1×10¹⁵ atoms/cm² to 4×10¹⁶atoms/cm², and thereby forming an amorphous layer.

In the ion implantation for the first time (first ion implantation),oxygen is ion-implanted in the surface layer of the silicon wafer at thetemperature of 200° C. or higher and the oxygen ion implantation amountof 1×10¹⁵ atoms/cm² to 4×10¹⁷ atoms/cm². Thereby, the oxygenion-implanted layer is formed in the wafer surface layer. In thesubsequent ion implantation for the second time (second ionimplantation), the amorphous layer is formed on the wafer surface sideof the oxygen ion-implanted layer at the temperature of less than 200°C. and the oxygen ion implantation amount of 1×10¹⁵ atoms/cm² to 4×10¹⁶atoms/cm². Thereafter, epitaxial growth is performed on the siliconwafer, and thereby a sequentially stacked two-layered incompleteimplanted oxide film is formed in the wafer surface layer. Under the ionimplantation conditions, the incomplete implanted oxide film does notonly include the ion-implanted layer, but also the amorphous layer as apart of a structured body. Thereby, the amorphous layer increases theoxygen deposition amount.

A vertical placement of the oxygen ion-implanted layer and the amorphouslayer may be flexible. The oxygen ion-implanted layer may be providedupper or lower to the amorphous layer. Since damage is formed more onthe wafer surface layer side than on the oxygen ion-implanted layer,however, the amorphous layer is generally provided as an upper layer. Inthe second ion implantation, oxygen ions are implanted to a depthsubstantially same as the oxygen ion-implanted layer of the wafersurface layer.

A thickness of the oxygen ion-implanted layer is 0.025 μm to 0.25 μm.When the thickness is less than 0.025 μm, the film cannot functionsufficiently as an end point detector at the time of thinning of thesilicon wafer. When the thickness exceeds 0.25 μm, the oxygen ionimplantation time is extended, thus causing reduction in productivity ofthe epitaxial wafer and leading to cost increase. A thickness of theamorphous layer is 0.025 μm to 0.25 μm. When the thickness is less than0.025 μm, the film cannot function sufficiently as an end point detectorat the time of thinning of the silicon wafer. When the thickness exceeds0.25 μm, the oxygen ion implantation time is extended, thus causingreduction in productivity of the epitaxial wafer and leading to costincrease.

The oxygen ion implantation in the silicon wafer surface layer herein isperformed in a modified low dose method (MLD) of the SIMOX wafer. Themodified low dose method performs the last oxygen ion implantation at alow dosage at proximate ambient temperature in the low dose SIMOXmethod, so as to form an amorphous layer; and thereby allows a buriedoxide layer to be formed at a lower dose. When the silicon wafer heatingtemperature in the first ion implantation is less than 200° C., damageat the time of oxygen implantation remains in the wafer surface layer. Apreferable heating temperature in the first ion implantation is 300° C.to 600° C. When the oxygen ion implantation amount in the first ionimplantation is less than 1×10¹⁵ atoms/cm², the film cannot functionsufficiently as an end point detector at the time of thinning of thesilicon wafer. When the implantation amount exceeds 4×10¹⁷ atoms/cm²,the oxygen ion implantation time is extended, thus causing reduction inproductivity of the epitaxial wafer and leading to cost increase.

When the silicon wafer heating temperature in the second ionimplantation exceeds 200° C., the amorphous layer is not formed due toinsufficient damage in the wafer surface layer at the time of ionimplantation. A preferable heating temperature in the second ionimplantation is an ambient temperature to 100° C. Within the range, ionimplantation damage can be caused that enables the amorphous layer to beformed in the wafer surface layer. When the oxygen ion implantationamount in the second ion implantation is less than 1.0×10¹⁵ atoms/cm²,the amorphous layer is not formed due to insufficient damage in thewafer surface layer at the time of ion implantation. When theimplantation amount exceeds 4×10¹⁶ atoms/cm², the oxygen ionimplantation time is extended, thus causing reduction in productivity ofthe epitaxial wafer and leading to cost increase. An epitaxial growthtemperature is 1,000° C. to 1,200° C. When the temperature is less than1,000° C., crystallinity of the epitaxial film is deteriorated. When thetemperature exceeds 1,200° C., a slip is likely to form in the externalperipheral portion of the wafer.

The present invention relates to the production method of the epitaxialwafer, in which the heat treatment is performed at a heating temperatureof the silicon wafer of 900° C. to 1,200° C. and a heating time of 0.5to 4 hours.

When the annealing temperature is less than 900° C., an oxygendeposition amount is low in the area in which oxygen is ion-implanted.When the temperature exceeds 1,200° C., a special annealing furnace isrequired for ultra-high temperature annealing. When the annealing timeis less than 0.5 hour, the oxygen deposition amount is low in the areain which oxygen is ion-implanted. When the time exceeds 4 hours,productivity of the epitaxial wafer reduces, thus incurring costincrease.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. [1] A cross-sectional view including a partial enlarged view of anepitaxial wafer according to a first embodiment of the present invention

FIG. [2] A cross-sectional view illustrating an ion implantation processin a production method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [3] A cross-sectional view illustrating an epitaxial growth processin the production method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [4] A cross-sectional view illustrating a device forming process inthe production method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [5] A cross-sectional view illustrating a wafer bonding process inthe production method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [6] A graph illustrating change in polishing torque when apolishing cloth comes in contact with an incomplete oxide film insurface polishing of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [7] A graph illustrating a relationship between an oxygen ionimplantation amount in a silicon wafer and a heat treatment condition inthe production method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [8] A graph illustrating change in polishing torque when apolishing cloth comes in contact with an insufficient incomplete oxidefilm in surface polishing of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [9] A cross-sectional view illustrating a thinning process in theproduction method of the epitaxial wafer according to the firstembodiment of the present invention

FIG. [10] A cross-sectional view of an epitaxial wafer according to asecond embodiment of the present invention

FIG. [11] A cross-sectional view illustrating a first ion implantationprocess in a production method of the epitaxial wafer according to thesecond embodiment of the present invention

FIG. [12] A cross-sectional view illustrating a second ion implantationprocess in the production method of the epitaxial wafer according to thesecond embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

An epitaxial wafer according to a first embodiment of the presentinvention and a production method of the same are explained below. A CISepitaxial wafer is used herein as an example.

In order to produce an epitaxial wafer 10, which is an epitaxial waferaccording to the first embodiment of the present invention, as shown inFIGS. 1 to 6, oxygen is first ion-implanted in a silicon wafer 11 from asurface thereof. Thereafter, the silicon wafer 11 is heat-treated, andthen an incomplete implanted oxide film 12 is formed in a surface layerof the silicon wafer 11, the incomplete implanted oxide film 12 beingmixedly provided with silicon particles a and silicon oxides b. Thereby,an active layer 13 is formed on a surface side of the silicon wafer 11relative to the incomplete implanted oxide film 12, and an epitaxialfilm 14 is grown on the surface of the silicon wafer 11.

The epitaxial wafer 10 is explained in detail below. The silicon wafer11 has a thickness of 775 μm, a diameter of 300 mm, and an axisdirection of a main surface is <100>. The silicon wafer 11 is producedby sequentially performing processes below. Specifically, a siliconmonocrystalline body is pulled from a melt of silicon in a crucible in aCZ method; subsequently, the silicon monocrystalline body is cut intoblocks, which are ground on an external periphery, and then sliced intonumerous wafer slices by a wire saw. Subsequently, each of the waferslices is chamfered, lapped, etched, polished, and washed.

An ion implantation process (FIG. 2) is then performed, in which theresultant silicon wafer 11 is implanted with oxygen ions from thesurface of the silicon wafer 11, and thus an ion-implanted layer 15 isformed in the surface layer of the silicon wafer 11. Immediately afterthe ion implantation process, the silicon wafer 11 is inserted into achamber (epitaxial growth furnace) 30 of an epitaxial growth device, andthus the epitaxial film 14 is grown on the surface of the silicon wafer11. Concurrently, the ion-implanted layer 15 is heat-treated, andthereby the incomplete implanted oxide film 12 is formed in the wafersurface layer, the incomplete implanted oxide film 12 being mixedlyprovided with the silicone particles a and the silicone oxides b.Further, an epitaxial growth process (FIG. 3) is sequentially performed,in which the active layer 13 is formed on the surface side of thesilicon wafer 11 relative to the incomplete implanted oxide film 12.

In the ion implantation process, the silicon wafer 11 is inserted intoan ion implantation device. Oxygen is then ion-implanted in the surfacelayer of the silicon wafer 11 from the wafer surface at a wafer heatingtemperature of 400° C., an implantation energy of 50 keV, and animplantation amount of 1.5×10¹⁷ atoms/cm². Thereby, the ion-implantedlayer 15 is formed at a depth of 0.1 μm from the surface of the siliconwafer 11, the ion-implanted layer 15 having low grade oxides, such asSiO, Si₂O₃, and the like.

In the epitaxial growth process, the silicon wafer 11 is placed in areactor of a sheet-fed vapor phase epitaxial growth device, whereby theepitaxial film 14 is grown on the surface of the silicon wafer 11 in avapor phase epitaxial method. The vapor phase epitaxial growth devicehas a susceptor 161 placed horizontally in a middle portion of thechamber 30, the susceptor 161 having a circular shape from a plan view,the chamber 30 being provided with heaters at vertical positions. Arecess-shaped wafer housing 171 is provided in a middle portion of asurface of the susceptor 161, the wafer housing 171 housing the siliconwafer 11 having front and rear surfaces in a horizontal state. A pair ofgas supply inlets are provided in one side portion of the chamber 30,the gas supply inlets flowing a predetermined carrier gas (H₂ gas) and apredetermined source gas (SiHCl₃ gas) in parallel with the wafer surfacein an upper space of the chamber 30. Further, a gas discharge outlet ofthe both gases is provided on the other side portion of the chamber 30.

At the time of the epitaxial growth, the silicon wafer 11 is firstplaced in the wafer housing 171 of the susceptor 161, such that thefront and rear surfaces of the wafer are provided horizontally.Subsequently, the carrier gas and the source gas are supplied to thereactor through the associated gas supply inlets. A reactor insidepressure is set to 0.1 KPa. Silicon, which is produced in pyrolysis orreduction of the source gas, is deposited at a reaction rate of 2μm/minute on the silicon wafer 11 heated to a high temperature of 1,100°C. Thereby, the silicon monocrystalline epitaxial film 14 having athickness of 5 μm is grown on the surface of the silicon wafer 11.

Concurrently, the ion-implanted layer 15 is heat-treated as the wafer isheated at the time of the epitaxial growth. Thereby, the incompleteimplanted oxide film 12 is formed having the silicon oxides b and thesilicon particles a mixed at a predetermined proportion, the siliconoxides b including deposited oxides, zonal oxides, and the like formedfrom SiO_(x) including SiO₂, the silicon particles a being granulatedsilicon in the silicon wafer 11 due to oxygen ion implantation. Theincomplete implanted oxide film 12 has a thickness of 0.1 μm. Inaddition, the active layer 13 having a thickness of 0.05 μm is formed onthe surface side of the silicon wafer 11 relative to the incompleteimplanted oxide film 12. Since the active layer 13 and the epitaxialfilm 14 are formed from the same silicon, the active layer 13 and theepitaxial film 14 are integrated. Thereby, the epitaxial wafer 10 isproduced.

The resultant epitaxial wafer 10 is then transferred to a device formingprocess. In the process, a predetermined photo process is performed onthe surface of the epitaxial film 14, and thus a device 151 is formed(FIG. 4). Thereafter, the silicon wafer 11 having a diameter of 300 mmand a thickness of 775 μm is attached to the surface of the epitaxialfilm 14 (FIG. 5). The rear side of the epitaxial wafer 10 is thenground, polished, and reduced in the thickness. In the process, theincomplete implanted oxide film 12 functions as an oxide layer thatselectively removes the epitaxial wafer 10. Specifically, when thethinning of the wafer proceeds to the incomplete implanted oxide film12, the incomplete implanted oxide film 12 serves as a polishingstopper. When the surface polishing of the wafer reaches the siliconoxides, a polishing cloth slips as it comes in contact with theincomplete implanted oxide film 12. At the time, polishing torque of apolisher is reduced. Detecting the reduced polishing torque allowsdetection of the time to stop polishing (a graph in FIG. 6).

A graph of FIG. 7 shows an oxygen ion implantation condition for formingthe incomplete implanted oxide film 12 and an annealing condition of thesilicon wafer 11. In the graph of FIG. 7, an area of the condition forforming the incomplete implanted oxide film 12 is indicated with areas Band C. In area A, a reduction in polishing torque cannot be clearlydetected, since the incomplete implanted oxide film 12 is notsufficiently formed, as shown in a graph of FIG. 8. Area D indicates anarea of a complete implanted oxide film formed on the conventionalepitaxial SIMOX wafer.

In the thinning of the wafer, etching may be employed in lieu ofgrinding and polishing of the epitaxial wafer 10. In this case, theincomplete implanted oxide film 12 functions as an etching stopper.Etching may be performed in a wet etching or dry etching method. When anHF/HNO₃/CH₃COOH solution or an alkaline solution (KOH, for example) isused in the wet etching method, an etching rate is reduced at the timewhen etching reaches the incomplete implanted oxide film 12 from thesilicon wafer 11. The etching rate is reduced because the rate isdifferent between silicon and silicon oxides due to material properties.The film thickness needs to be monitored, however, since the stopfunction of the incomplete implanted oxide film 12 in wet etching is notperfect.

Examples of dry etching include a method in which material is aerated ina reaction gas (reactive gas etching), a reactive ion etching method inwhich a gas is ionized or radicalized by plasma, and the like.Generally, XeF₂ is used for reactive gas etching, and SF₆, CF₄, and CHF₃are used for reactive ion etching. An applicable plasma generationmethod can be classified into capacitive coupling, inductive coupling,ECR-RIE, and the like. An exposed incomplete implanted oxide film, whichis not a complete silicon oxide film, can be removed by polishing.Alternatively, it is also possible to perform oxidation and heattreatment at a temperature of 600° C. to 1,000° C. for about 1 to 30minutes so as to produce complete silicon oxides, and then performremoval using an HF solution. Thereby, the CIS epitaxial wafer 10implanted with the device 151 on the rear side of the epitaxial film 14(a space sandwiched by the silicon wafer 11; FIG. 9).

For the epitaxial wafer 10 of the first embodiment, the oxygen ionimplantation amount is reduced compared with a case of the implantedoxide film of the conventional epitaxial SIMOX wafer (2.5×10¹⁷atoms/cm²), as described above. Further, the ion-implanted layer 15 isheat-treated at the time of the epitaxial growth, when the temperatureis lower (1,100° C.) than conventional high temperature annealing(1,350° C.).

Thereby, the incomplete implanted oxide film 12 is formed in the surfacelayer of the silicon wafer 11. Unlike the conventional implanted oxidefilm sequentially provided with silicon oxides b, the film thickness ofthe incomplete implanted oxide film 12 thus hardly increases along withoxidation of silicon. Consequently, even when ions are implantedpresumptively when particles are deposited on the wafer surface, andthus the oxide film breaks in the wafer surface layer, a pit can beprevented from forming in the wafer surface, and eventually from formingin the surface of the epitaxial film 14 grown on the wafer surface.Thereby, a surface defect of the epitaxial film 14 can be prevented, thesurface defect being caused by deposition of particles on the wafersurface at the time of oxygen ion implantation. Further, the oxygen ionimplantation amount is less compared with the conventional epitaxialSIMOX wafer, and high temperature annealing is eliminated. Thus, costcan be reduced compared with the epitaxial SIMOX wafer.

In addition, since a temperature distribution in the wafer surface iseven, no difference is caused in the growth rate of the epitaxial film14 in the wafer surface at the time of the epitaxial growth, thedifference being between in the area provided with the implanted oxidefilm 12 and in the remaining area of the external peripheral portion ofthe wafer. Different from the conventional epitaxial SIMOX wafer, it isthus unlikely that the film thickness increases in the externalperipheral portion of the epitaxial film 14, and thereby a slip can beprevented from forming in the external peripheral portion of the wafer.Further, the incomplete implanted oxide film 12 also serves as agettering site of metal impurities contained in the silicon wafer 11.Thus, the silicon wafer 11 as well as a device can be prevented frommetal contamination.

An epitaxial wafer according to a second embodiment of the presentinvention and a production method of the same are explained below, withreference to FIGS. 10 to 12. As shown in FIGS. 10 to 12, an epitaxialwafer 10A according to the second embodiment of the present inventionundergoes a first ion implantation process and a second ion implantationprocess. The first ion implantation process forms an oxygenion-implanted layer 17 as a lower layer; the second ion implantationprocess forms an amorphous layer 18 as an upper layer. The both layers17 and 18 are integrated at the time of heat treatment, and thusprovided as a substantially one-layer incomplete implanted oxide film12.

The ion-implanted layers 17 and 18 having a two-layer structure areproduced as described below. Specifically, the first ion implantationprocess is first performed, in which oxygen is ion-implanted in asurface layer of a silicon wafer 11 from a wafer surface, at a waferheating temperature of 400° C., an implantation energy of 216 keV, andan implantation amount of 1.2×10¹⁷ atoms/cm². Thereby, the oxygenion-implanted layer 17 is formed at a depth of 0.5 μm from the surfaceof the silicon wafer 11 (FIG. 11).

Subsequently, the second ion implantation process is performed on thesilicon wafer 11. Specifically, oxygen is ion-implanted in the surfacelayer of the silicon wafer 11 from the wafer surface, at a wafer heatingtemperature of 40° C., an implantation energy of 216 keV, and animplantation amount of 4×10¹⁵ atoms/cm². Thereby, the amorphous layer 18is formed at a depth of 0.4 μm from the surface of the silicon wafer 11(on an upper side of the oxygen ion-implanted layer 17; FIG. 12).Thereafter, the epitaxial growth process of the first embodiment isperformed on the silicon wafer 11. Thereby, the substantially one-layerincomplete implanted oxide film 12 having a thickness of 0.2 μm isformed at a depth of 5.3 μm from the wafer surface. The structure aboveincreases the thickness of the incomplete implanted oxide film 12. Otherstructures, functions, and effects are substantially same as those inthe first embodiment, and thus explanations thereof are omitted.

A production method of an epitaxial wafer according to a thirdembodiment of the present invention is explained below. In theproduction method of an epitaxial wafer 10 according to the thirdembodiment of the present invention, a process for implanting oxygenions in a silicon wafer 11 is performed only once, similar to the firstembodiment. Immediately after an epitaxial growth process, an annealingprocess is performed, in which the silicon wafer 11 is heated underpredetermined conditions. Thereby, the incomplete implanted oxide film12, which was insufficient after the epitaxial growth, turns into theappropriate incomplete implanted oxide film 12 after undergoing theannealing process subsequent to the epitaxial growth.

The epitaxial growth is performed at a heat treatment temperature of1,150° C. for a heat treatment time of 3.5 minutes. Further, theannealing is performed at a heat treatment temperature of 1,200° C. in1% oxygen gas atmosphere for a heat treatment time of 30 minutes. Asdescribed above, the ion implantation process is performed only once;subsequently, the heat treatment is performed twice; and thereby, theincomplete implanted oxide film 12 is formed. Thus, the epitaxial filmhaving a low oxygen deposition amount and a small surface roughness canbe produced. The annealing process subsequent to the epitaxial growthprocess may be performed immediately prior to the epitaxial growthprocess under the same annealing conditions. In this case, oxygendeposited in the annealing process serves as a gettering site, thusallowing production of a high quality epitaxial film. Other structures,functions, and effects are substantially the same as those in the firstembodiment, and thus explanations thereof are omitted.

A production method of an epitaxial wafer according to a fourthembodiment of the present invention is explained below. In theproduction method of an epitaxial wafer 10A according to the fourthembodiment of the present invention, a process for implanting oxygenions in the silicon wafer 11 is performed twice, similar to the secondembodiment (the first ion implantation process for forming the oxygenion-implanted layer 17 and the second ion implantation process forforming the amorphous layer 18). In addition, an annealing process isperformed, in which the silicon wafer 11 is heated under predeterminedconditions, immediately after an epitaxial growth process.

The epitaxial growth is performed at a heat treatment temperature of1,150° C. for a heat treatment time of 3.5 minutes. Further, theannealing is performed at a heat treatment temperature of 1,200° C. inargon gas atmosphere for a heat treatment time of 4 hours. As describedabove, the ion implantation process is performed twice; subsequently,the heat treatment is performed twice; and thereby, the incompleteimplanted oxide film 12 is formed. Thus, the epitaxial film having a lowoxygen deposition amount and a small surface roughness can be produced.The annealing process subsequent to the epitaxial growth process may beperformed immediately prior to the epitaxial growth process under thesame annealing conditions. In this case, oxygen deposited in theannealing process serves as a gettering site, thus allowing productionof a high quality epitaxial film. Other structures, functions, andeffects are substantially the same as those in the second embodiment,and thus explanations thereof are omitted.

Industrial Applicability

The present invention is effective, for example, as a CIS epitaxialwafer.

1. An epitaxial wafer comprising: a silicon epitaxial film grown on asurface of a silicon wafer; and an incomplete implanted oxide filmhaving a predetermined thickness and being mixedly provided with apredetermined ratio of silicon particles and silicon oxides in an areahaving a depth of 0.05 μm to 0.5 μm from the surface of the siliconwafer, the silicon oxides consisting of SiO_(x)including SiO₂, thesilicon particles comprising granulated silicon in the silicon waferproduced by an oxygen ion implantation, and the incomplete implantedoxide film being provided with a silicon oxide film intermittentlyformed in an entire area of an ion-implanted layer for the ionimplantation.